Field of the Invention
The invention relates to a controller for a device in a motor vehicle, in particular for a motor vehicle transmission, by means of which the transmission ratio is automatically controlled in dependence on at least the accelerator pedal position and the driving speed, using stored characteristic maps or fields, and which has a fuzzy logic circuit with a rule base, by means of which the various signals characterizing driving states and the load state of the motor vehicle are evaluated and control signals are then generated which define the transmission ratio. Such a controller can be used in a motor vehicle, for example for controlling an automatic transmission, rear-wheel steering, traction control or a driving speed controller.
In prior art transmission controls for motor vehicles, the transmission ratio of the transmission is automatically set as a function of the accelerator pedal position and of the driving speed, using stored characteristic maps or fields. At the same time, various driving parameters and operating states of the motor vehicle are taken into account (see, for instance, European patent applications EP-A 0576703, EP-A 0622570, EP-A 0626527, EP-A 0638742). The selection of the gear to be shifted in each case or--in the case of continuously variable transmissions--the transmission ratio to be set is performed by control circuits which operate in accordance with the methods of fuzzy logic. Using this logic, expert knowledge which has been obtained through experience is described in the form of a so-called rule base and hence used for the open-loop or closed-loop control operations of the motor vehicle transmission. Control signals are generated, for example a load signal and a driver recognition signal, which effect a changeover of the characteristic map, as well as gear-shifting blocking signals which prevent shifts which are brought about by gear-shifting characteristic maps, but could lead to dynamically unfavorable driving states (for example to a risk of skidding).
In certain dynamic driving states it may also be expedient to shift up or down--or to appropriately adjust the transmission ratio--which would not be brought about by the gear-shifting or actuating characteristic map that is active at present. Examples of such dynamic driving states are the occurrence of inadmissible wheel brake slip or driving down relatively long downhill gradients.